High speed print hammer with dynamic damper means

ABSTRACT

A hammer for impact printers having a hammer arm with a striking face mounted for movement toward and away from type to cause a document located between the hammer face and type to be printed when the hammer arm is propelled toward the type. The hammer arm is supported by two spring reeds and is cocked away from the printing position against a permanent magnet. Printing is effected by opposing the permanent magnetic field with an electromagnetic field to release the cocked hammer arm. The spring reeds cause the hammer to be propelled toward the type. A dynamic damper supported by another spring reed is cocked with the hammer arm. The natural frequency of the damper is lower than that of the hammer arm, causing the damper to strike the rebounding hammer arm after printing. The energy in the rebounding hammer arm is absorbed by the impact of the damper to reduce oscillations in the hammer arm.

United States Patent 1 Curtiss et al.

1 HIGH SPEED PRINT HAMMER WITH DYNAMIC DAMPER MEANS [75] Inventors: Robert H. Curtiss,.Wayland; Richard Holzman; Seldan A. Lazarow, both of Framingham, all

of Mass.

[73] Assignee: Nortec Computer Devices Inc.,

Ashland, Mass.

[22] Filed: Sept. 2, 1969 [21] Appl. No.: 854,531

Ponzano l01/93C Staller 101/93 C Dec. 25, 1973 Primary Examiner-Robert F. Pulfrey Assistant Examiner-E. M. Coven AttorneyDaniel M. Rosen 57 ABSTRACT A hammer for impact printers having a hammer arm with a striking face mounted for movement toward and away from type to cause a document located between the hammer face and type to be printed when the hammer arm is propelled toward the type. The hammer arm is supported by two spring reeds and is cocked away from the printing position against a permanent magnet. Printing is effected by opposing the permanent magnetic field with an electromagnetic field to release the cocked hammer arm. The spring reeds cause the hammer to be propelled toward the type. A dynamic damper supported by another spring reed is cocked with the hammer arm. The natural frequency of the damper is lower than that of the hammer arm, causing the damper to strike the rebounding hammer arm after printing. The energy in the rebounding hammer arm is absorbed by the impact of the damper to reduce oscillations in the hammer arm.

11 Claims, 3 Drawing Figures ADJUST FLIGHT TIME HIGH SPEED PRINT HAMMER WITH DYNAMIC DAMPER MEANS BACKGROUND OF THE INVENTION High speed impact printers require printing hammers which can be actuated at the precise time that the moving type is in the printing position.

The most commonly used hammers are electromagnetically operated by the application of relatively high power electrical pulses having precisely-controlled amplitudes and durations. Hammers are also driven electro-dynamically by passing electrical pulses through coils mounted on the hammer arms. As in the case of electromagnetically-driven hammers, electrodynamic hammers require accurately controlled pulse amplitudes and widths and are further complicated by the requirement of electrical connnections to the coils on the moving hammers.

The power required to activate hammers can be reduced by cocking the hammers with a mechanical force and then supplying a relatively small force to release the hammers from their cocked positions. When the hammers are released electrically, the amplitude and duration of the applied pulses are not as critical as in the caseof electromagnetically or electrodynamically driven hammers. When the hammers are cocked and then released, the hammers rebound after striking the type and often oscillate for a period of time, producing poor print quality of multiple impacts against the type.

The selection of hammer drive circuitry to provide the necessary electrical pulses is dependent upon the type of hammers used. An advantage of the cocked hammer design is that it permits the use of relatively low power hammer drives whose output pulses may be of short duration: long enough to release the hammersfrom their cocked positions, but not necessarily persisting during the entire flight time of the hammers. Since the pulse duration may be shorter, the hammer drivers may be time-shared between several hammers, reducing the cost of the electrical circuitry.

In the present invention, the cocked hammer technique is used, but in a manner to avoid the multiple impact problem while retaining the advantages of permitting low-power hammer drivers with minimum constraints of the shape of the electrical drive pulses. The multiple impact problem is solved by providing a dynamic damper which coacts with the rebounding arm to absorb its energy.

BRIEF DESCRIPTION OF THE INVENTION The type carrier is located in front of the document to be printed and may be a band, drum, chain or any other form of type carrier. The hammers are located behind the document, one for each character position along the line to be printed. Since the type moves continuously before the document, the hammers must be activated at precisely the time that the desired type characters are in position or the resultant printing will be misregistered.

In the preferred embodiment of the invention, each hammer contains a hammer arm-having a striking force at one end and a cocking surface at the other end. Each hammer arm is suspended for movement by two spring reeds, one at each end of the arm.

A single permanent magnet is sandwiched between two comb-shaped pole pieces to provide a pair of poles behind each hammer arm cocking surface. Before a line is to be printed, a mechanical bail physically pushes all hammer arms away from their printing positions and their cocking surfaces are attracted to and held by the permanent magnet. The bail employs an electromagnetic clutch and a continuously reciprocating source of mechanical power.

Each pole is surrounded by a coil which, when provided with current, produces an electromagnetic field that opposes the field of the permanent magnet. When a selected hammer is to be activated, current is applied through the coils on its two poles.

Each hammer also contains a dynamic damper consisting of a mass supported by a spring reed. When the hammer is in its rest position between the printing position and the cocked position, the damper mass rests against a lip on the hammer arm. When the hammer is cocked, the lip forces the damper mass in the same direction, simultaneously cocking the damper.

When the cocked hammer arm and damper are released, the hammer arm moves toward the printing position in virtually frictionless free flight according to the natural frequency of the hammer arm and its supporting spring reeds. Since the hammer arm is initially cocked back further from its rest position than the distance between the rest position and the document, the released hammer strikes the document and rebounds. The dynamic damper is designed with a natural frequency that is lower than the natural frequency of the hammer arm by an appropriate amount to cause the damper mass to impact the lip on the hammer arm at about the same time that the rebounding hammer arm reaches its rest position. Thus, the energy of the rebounding hammer is absorbed by the impact with the damper mass and the hammer arm comes quickly to rest. Were it not for the impact of the damper mass, the hammer arm would swing past its rest position and again move toward the document, causing double striking of the document and resultant poor print quality.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION The preferred embodiment of the invention is illustrated in the drawings, where:

FIG. 1 is an isometric cut-away view of the invention,

FIG. 2 is a diagram showing the relative motion of the hammer arm and the dynamic damper, and

FIG. 3 is an isometric cut-away view of another embodiment of the invention.

To facilitate an understanding of the preferred embodiment of the invention, only one hammer is completely shown in FIG. I. Each hammer contains a hammer arm 11 supported for movement along its length by two spring reeds 13. The reeds are supported by a frame 15. Each hammer arm contains a flat striking face 17 which is approximately perpendicular to the long dimension of the hammer arm. The hammer arms and spring reeds are preferably constructed of steel.

A type carrier 19, shown as a portion of a steel band, supports type (not shown) on its surface which faces the hammer arms. A document 21 is located between the hammer striking faces 17 and the type carrier 19. The type carrier moves continuously in the direction of the arrow along the line to be printed on the document so that each character in the font of type passes each hammer face. The hammers that are not shown on the drawing are aligned along the printing line and are suspended from adjacent frames 15, several of which are shown in the drawing.

Before beginning to print a line, all hammer arms are cocked by a bail bar 23 which extends along the entire length ofthe printing line. As described in detail below, the bail bar rotates in a counterclockwise direction about a shaft 25. The edge of the bail bar 23 contacts a cocking portion 27 on each hammer arm 11, forcing the hammer arms toward the left until the cocking portions 27 contact pairs of piles 29. The bail bar is then rotated in a clockwise position back to its inactive position (the position shown in FIG. I).

A permanent magnet 31 extends along the length of the printing line and is supported between two poles pieces 33. The magnet is preferably the type known as a rubber magnet, which employs powdered barium ferrite vulcanized in rubber. Each pole piece 33 is comb-shaped, containing a pole 29 for each hammer in the printer. Thus, before printing each line, all hammer arms 11 are moved away from their rest positions (as shown) to cocked positions where the cocking portions 27 contact the permanent magnet poles 29. The field of the permanent magnet maintains the hammer arms in the cocked position as the bail bar 23 is returned to its inactive position.

Each hammer also contains a dynamic damper consisting of a damper mass 35 supported by a spring reed 37 to the corresponding frame 15. In the rest position, as shown in FIG. 1, the hammer face 17 is slightly spaced from the document 13 and the right surface of thedamper mass 35 lightly contacts the left surface of a damper lip 39. A layer of high molecular weight polyethylene is bonded to the impacting (right) surface of the damper mass 35 to cushion the impact between the damper mass and the lip 39 on the hammer arm.

When the hammer arm is cocked toward the left against the poles 29, the damper lip 39 faces the damper mass 35 in the same direction. Thus, cocking of the hammer arm prior to printing also causes the damper mass to be cocked.

A coil 41 is mounted on each pole 29, although only one such coil is shown in the drawing. Thus, there are two coils 41 corresponding to the two poles 29 for each hammer.

A hammer is actuated by supplying a sharp pulse of current through leads 43 to both coils 4] corresponding to the selected hammer. The coils develop an electromagnetic field which opposes the permanent magnetic field, releasing the hammer arm from its cocked position. As shown in FIG. 2 by a heavy solid line 45, the hammer face moves from its cocked position (about 0.2 inch) past its rest position to its impact position (about 0.08 inch past the rest position). A heavy dashed line 47 shows the path that the hammer face would assume, were there no impact. The path is a damped cosinusoidal waveshape. Upon impact, the hammer rebounds as shown by the heavy solid line 49 toward its rest position. The light solid line 51 shows the path taken by the damper mass 35. The natural resonant frequency of the damper mass and its supporting reed is lower than the natural resonant frequency of the hammer arm and its supporting reeds by an amount such that the damper mass reaches its rest position at about the time that the hammer arm reaches its rest position after rebounding from its impact against the document. At this time, the damper mass 35 strikes the damper lip 39 and the kinetic energy of both the hammer arm and the damper mass is largely converted to thermal energy in the polyethylene cushion on the face of the damper mass. Thus, the motion of the hammer arm and the damper mass terminate as shown in F IG. 2 by the line 53. In practice, it is not possible to provide complete termination of all movement of the hammer arm, but the motion of the hammer arm is sufficiently diminished to avoid oscillations that would cause double impact against the document.

The flight time of the hammer arm 11 (and, hence, its speed and force at impact) is controlled by adjusting the position of the frame 15 by an adjustment mechanism 55. The flight time of the hammer arm is increased bymoving the frame 15 away from the document and is decreased by moving the frame toward the document. The flight time adjustment is made individually for each hammer while the printer is in operation based upon observation of the registration of the printing in the corresponding printing position on the document. When the type carrier 19 is a belt, chain, reciprocating bar or other device providing movement of the type along the direction of the printing line, errors in flight time adjustment cause the printing to be misregistered (unevenly spaced) along the printing line. When the type carrier is a drum, errors in flight time adjustment cause the printing to be misregistered in the vertical direction. It is also possible to simultaneously adjust the flight time of all hammers to control print density in order to compensate for variations in document thickness of the number of copies to be printed.

As indicated above, the hammer arms 11 are cocked before printing by the counterciockwise rotation of the bail bar 23 about shaft 25. The bail bar is rigidly connected to the shaft by several bail bar support arms 57, one of which is shown in FIG. I. A bail drive arm 59 is also rigidly connected to the shaft 25. The other end of the bail drive arm is rotatably connected to a clutch driven element 61 through a shaft 63. A spring 64 biases the driven element 61 toward its inactive position, as shown in FIG. 1. A clutch drive plate 65 continuously reciprocates toward and away from the driven element 61. A guide rod 66 reciprocates in a bearing 67 in the center of the driven element 61 to guide the relative positions of the clutch elements 61, 65. A motor, not shown, continuously rotates a shaft 69 mounted in a housing 71. An eccentric cam 73 is rigidly mounted on the shaft 69. The cam revolves in a bearing plate 75 which is rigidly connected to the dirve element 65. Thus, revolution of the eccentric cam 73 causes the drive element 65 to move away from (as shown in FIG. 1) and toward the driven element 61.

The clutch is operated by applying current through a pair of leads 77 to an electromagnet coil in the driven element 61 at a time slightly before the drive element 65 reaches the driven element. The electromagnetic field thus developed attracts the drive element 65, pulling the driven element 61 as the drive element reverses direction. Current to the electromagnetic coil is terminated at the time that the drive element 65 completes one full reciprocation (after one revolution of the shaft 69 and cam 73). The driven element 61 is then maintained at its rest position by the spring 64. The bail bar cocks the hammer arms through the interconnecting linkage during the first half of the cycle (while the driven element is being pulled). The bail bar is returned to its inactive position during the second half of the cy- .cle.

The inventive hammer has been described with respect to the preferred embodiment shown in FlG. 1. The hammer is also suitable for use in other environments, such as in the printer shown in FIG. 3, in a paper tape punch, a card punch, or in any other device requiring an accurately-timed mechanical force of the type provided.

In the alternative embodiment shown in FIG. 3, a printer employs a hammer of the type described with respect to FIG. 1, but the striking face 17 of the hammer 11 directly impacts the type carrier 19. The type carrier is comb-shaped with the type 79 formed on the flexible extensions 81 of the comb. Thus, the hammer forces the type against the document 21, in contrast to the embodiment of FIG. 1, where the hammer forces the document against the type.

In both embodiments of the invention, a ribbon is located between the type and the document of pressuresensitive paper is used. The invention primarily lies in the construction of the hammer and is not specifically related to the type of documents employed, or to the specific construction of the type carrier.

What is claimed is:

1. In a printer, the combination comprising a hammer assembly having a cocked position, a rest position and an impact position, said hammer assembly including a support, a hammer arm having an impact face and a damping lip on opposing portions of said hammer arm, a damping mass having an impact face, first spring means having a first natural frequency coupling said arm to said support, second spring means having a second natural frequency less than said first natural frequency, and coupling said damping mass to said support, said second spring means supporting said damping mass impact face adjacent said damping lip, means for moving said hammer arm from said rest position to said cocked position and tensing said first spring means, said hammer arm damping lip moving said damping mass from said rest position to said cocked position and tensing said second spring means, means for releasing said hammer arm and damping mass for movement in accordance with the energy stored in said first and second spring means from said cocked position to said impact position, said hammer arm moving at a first rate determined by the natural frequency of said first spring means, and said damping mass moving at a second rate lower than said first rate and determined by the natural frequency of said second spring means, impacted means, said hammer arm impact face imparting said impacted means in said impact position and rebounding therefrom, said damping mass impact face and said hammer arm damping lip colliding at said rest position, thereby substantially damping the movement of both said damping mass and said hammer arm.

2. The printer described in claim 1, wherein said first spring means comprises two flexible reeds substantially perpendicular to the direction of movement of said hammer arm.

3. The printer described in claim 2, wherein said second spring means is a flexible reed that is substantially parallel to said two flexible reeds.

4. The printer described in claim 2, wherein said springs are flexible reeds that bias said hammer arm to its rest position.

5. The printer described in claim 1, wherein the hamme'r arm is biased toward its rest position, cocking means wherein said hammer arm is initially cocked away from its rest position, means for supplying a steady magnetic force to maintain said hammer arm in its cocked position, and means for opposing the steady magnetic force with a momentary magnetic force to release said hammer arm from its cocked position toward impact.

6. The printer described in claim 5, wherein said cocking means comprises a continuously reciprocating bail and a cocking arm which is controllably clutched to the bail by magnetic means.

7. The printer described in claim 1, wherein said hammer assembly is adjustable in the direction of movement of said hammer arm to control the rest position of said hammer arm, whereby the flight time, speed and impact force of the hammer arm are controllable.

8. The printer described in claim 1, wherein said impacted means includes typepresenting means, and said type-presenting means moves along a line to be printed and is adapted to print on a document located between said hammer face and said type-presenting means.

9. The printer described in claim 1, wherein said type-presenting means moves along a line to be printed and is adapted to print on a document located on the side of said type-presenting means opposite to the side impacted by said hammer face.

10. The printer described in claim 9, wherein the type-presenting means is comb-shaped with flexible extensions that support the type.

11. For use with a printer, a hammer assembly, said hammer assembly comprising a support, a hammer arm, said hammer arm having an impact face and a damping lip on opposite surface portions thereof, first spring means mounting said arm to said support, a damping mass, said damping mass including an impact face positioned proximate to said damping lip on said hammer arm, second spring means coupling said damping mass to said support, said second spring having a lower natural frequency than said first spring, said printer including first means for moving said hammer arm and said damping mass to a cocked position relative to said support, thereby storing energy in said first and second spring means, second means for releasing said hammer arm from said cocked position, said hammer and damping mass undergoing a resultant movement caused by release of the energy stored in said first and second spring means, an impacted means, said impacted means positioned so as to be impacted by the impact face of said hammer arm, said hammer arm rebounding after said impact in a direction opposite said forward motion, said damping mass and said damping lip colliding, said collision damping the movement of both said damping mass and said hammer arm.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 3, Dated December 25,

lnv Robert H. Curtiss, et a1,

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 30, change"drive" to -driver--; line 34, change "drives" to --driversline 47, insert --hammer-- between "rebounding" and "arm";

line 61, change "force" to --face--,

Column 2, line 31, delete "same".

Column 3, line 10, change "piles" to --poles--;

line 38, change "faces" to "forces",

Column 4, line 31, change the first "of" to --t-or--;

line 50, change "dirve" to --drive--,

Column 5, line 14, delete the second "the";

line 20, change "of" to "or",

Signed and sealed this 22nd day of April 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks F ORM PC4050 (10-69) USCOMM-DC 60376-P69 uls. sovimmzm "mums omen: 930 

1. In a printer, the combination comprising a hammer assembly having a cocked position, a rest position and an impact position, said hammer assembly including a support, a hammer arm having an impact face and a damping lip on opposing portions of said hammer arm, a damping mass having an impact face, first spring means having a first natural frequency coupling said arm to said support, second spring means having a second natural frequency less than said first natural frequency, and coupling said damping mass to said support, said second spring means supporting said damping mass impact face adjacent said damping lip, means for moving said hammer arm from said rest position to said cocked position and tensing said first spring means, said hammer arm damping lip moving said damping mass from said rest position to said cocked position and tensing said second spring means, means for releasing said hammer arm and damping mass for movement in accordance with the energy stored in said first and second spring means from said cocked position to said impact position, said hammer arm moving at a first rate determined by the natural frequency of said first spring means, and said damping mass moving at a second rate lower than said first rate and determined by the natural frequency of said second spring means, impacted means, said hammer arm impact face imparting said impacted means in said impact position and rebounding therefrom, said damping mass impact face and said hammer arm damping lip colliding at said rest position, thereby substantially damping the movement of both said damping mass and said hammer arm.
 2. The printer described in claim 1, wherein said first spring means comprises two flexible reeds substantially perpendicular to the direction of movement of said hammer arm.
 3. The printer described in claim 2, wherein said second spring means is a flexible reed that is substantially parallel to said two flexible reeds.
 4. The printer described in claim 2, wherein said springs are flexible reeds that bias said hammer arm to its rest position.
 5. The printer described in claim 1, wherein the hammer arm is biased toward its rest position, cocking means wherein said hammer arm is initially cocked away from its rest position, means for supplying a steady magnetic force to maintain said hammer arm in its cocked position, and means for opposing the steady magnetic force with a momentary magnetic force to release said hammer arm from its cocked position toward impact.
 6. The printer described in claim 5, wherein said cocking means comprises a continuously reciprocating bail and a cocking arm which is controllably clutched to the bail by magnetic means.
 7. The printer described in claim 1, wherein said hammer assembly is adjustable in the direction of movement of said hammer arm to control the rest position of said hammer arm, whereby the flight time, speed and impact force of the hammer arm are controllable.
 8. The printer described in claim 1, wherein said impacted means includes type-presenting means, and said type-presenting means moves along a line to be printed and is adapted to print on a document located between said hammer face and said type-presenting means.
 9. The printer described in claim 1, wherein said type-presenting means moves along a line to be printed and is adapted to print on a document located on the side of said type-presenting means opposite to the side impacted by said hammer face.
 10. The printer described in claim 9, wherein the type-presenting means is comb-shaped with flexible extensions that support the type.
 11. For use with a printer, a hammer assembly, said hammer assembly comprising a support, a hammer arm, said hammer arm having an impact face and a damping Lip on opposite surface portions thereof, first spring means mounting said arm to said support, a damping mass, said damping mass including an impact face positioned proximate to said damping lip on said hammer arm, second spring means coupling said damping mass to said support, said second spring having a lower natural frequency than said first spring, said printer including first means for moving said hammer arm and said damping mass to a cocked position relative to said support, thereby storing energy in said first and second spring means, second means for releasing said hammer arm from said cocked position, said hammer and damping mass undergoing a resultant movement caused by release of the energy stored in said first and second spring means, an impacted means, said impacted means positioned so as to be impacted by the impact face of said hammer arm, said hammer arm rebounding after said impact in a direction opposite said forward motion, said damping mass and said damping lip colliding, said collision damping the movement of both said damping mass and said hammer arm. 